Interfacial processes for the polymerization of polycarbonate yield a mixture comprising an aqueous phase and an organic phase. The aqueous phase, also referred to as the brine phase, comprises salts, ionic species, and interfacial catalyst. The organic phase, also referred to as the resin phase or polymer phase, comprises solvent, dissolved polycarbonate, and interfacial catalyst. Some salts and ionic species can further be present in the organic phase as a result of brine entrainment from the aqueous phase. These salts and ionic species (referred to herein as “ions” for convenience), as well as any interfacial catalyst are generally removed from the organic phase in a purification process because they affect the final product quality. Such a purification process generally involves separation of the aqueous phase from the organic phase followed by the removal of ions and catalyst in one or more extraction steps from the organic phase to result in a purified polycarbonate.
A problem in polycarbonate purification processes is that the organic phase and the aqueous phase can form an emulsion during manufacture or purification. Emulsification is characterized by the creation of small, difficult-to-remove droplets of a first phase dispersed within a second phase. Accordingly, emulsification can result in one or both of 1) only a partial separation of the organic phase and aqueous phase such that part of the organic phase is carried over and remains with the aqueous phase and 2) an insufficient removal of impurities (such as ions and catalyst) from the organic phase. As a result, stable plant operation can be difficult to maintain and ultimately the quantity and the quality of the purified polycarbonate can be reduced.
A further problem that can arise in a polycarbonate manufacturing facility is the treatment of certain organic interfacial polycarbonate waste streams, also called “off-grade solvent.” These waste streams are generated in the interfacial polycarbonate manufacturing process through hood flushes to disc centrifuges, for example, and a variety of flushes to the equipment in various unit operations using an organic solvent. They will accordingly be referred to herein as “interfacial polycarbonate organic wash streams,” or “organic wash streams” for convenience. The interfacial organic polycarbonate wash stream contains low levels of dissolved solids that are often degraded polycarbonates, catalysts, and ions. Accordingly, without any treatment or without sufficient purification, recycle of the wash stream back to the reactor may adversely impact product properties such as color and melt stability. While, the wash stream can be purified by an aqueous wash, emulsification can be an issue affecting the efficiency of the treatment. In addition, the emulsified organic phase carryover, which is known as “cream,” can make its way to the wastewater treatment system and block the system, disrupting the entire process.
One or both of a purification process that can reduce or eliminate emulsion formation in interfacial polycarbonate manufacture and polymerization and that can reduce or eliminate emulsions in the purification of organic polycarbonate waste stream is therefore desirable.